Surface maintenance machines that perform a single surface maintenance or surface conditioning task are well known. Surface maintenance machines are generally directed to applications such as floor surfaces, or simply floors. The term floor, as used herein, refers to any support surface, such as, among others, floors, pavements, road surfaces, ship decks, and the like.
Many floor or surface maintenance machines are constructed having a sole surface conditioning machine or system so as to only sweep, others to scrub, while still others to polish or burnish. Other floor maintenance machines may be configured to perform multiple types of surface maintenance tasks. One example of a multi-task surface conditioning machine is disclosed in U.S. Pat. No. 3,204,280, entitled, “Floor Cleaning & Waxing Machine,” issued to Campbell. Another example is disclosed in U.S. Pat. No. 4,492,002, entitled, “Floor Cleaning Machine,” in name of inventors Waldhauser, et al. Disclosed therein is a forward sweeper assembly followed by a scrubber assembly that is followed by a squeegee assembly. Yet, another example of a multi-task floor conditioning machine is disclosed in a PCT application published at WO 00/74549, on Dec. 14, 2000, entitled, “Floor Cleaning Machine,” in name of inventors Thomas, et al.
Surface maintenance machines which perform a burnishing task generally include a scheme for controlling the degree of burnishing applied to a floor surface depending upon the type of floor surface. Such machines commonly include a driver assembly which includes a working appliance or tool, such as a pad or brush, affixed to a driver that is rotatably driven by a driver motor. The driver assembly is selectively raised and lowered by an actuator to achieve a desired force or pressure against a floor surface.
Surface maintenance machines which perform a scrubbing task also commonly include a driver assembly having a rotatable scrubber, such as a brush, pad, or the like, affixed to a scrubber head rotatably driven by a driver motor. The scrubber head typically is selectively raised and lowered by an actuator coupled to the driver to achieve a desired scrubbing force or pressure of the brush against a floor surface. Like burnishing machines, scrubbing machines generally include a scheme for controlling the scrubbing force or pressure applied to the floor surface. Examples of surface maintenance machines having scrubbing systems are taught in U.S. Pat. Nos. 4,757,566; 5,481,776; 5,615,437; 5,943,724; and 6,163,915.
Sweeper systems also are analogous to burnishing and scrubbing systems in that they too may include a rotatable sweeper tool (e.g., a brush) driven by a driver motor. Like burnishing and scrubbing systems, the sweeper system brush may be lowered and raised relative to a floor to achieve a desired sweeping result.
Schemes for controlling the burnishing/scrubbing/sweeping force typically employ a current sensor to monitor the current drawn by the driver motor. In such schemes, the sensed motor current may be used to control torque load on the driver motor such that a desired burnishing/scrubbing/sweeping force may be achieved. However, such schemes may not provide accurate control of the work output applied to the floor, because the voltage applied to the driver motor may vary, thus causing corresponding variations in speed and work output of the rotatable work tool. In accordance with other control schemes, a “pressure” sensor is employed that provides a signal that is representative of the pressure of the work tool against the floor. This signal also may be used to control torque load on the motor to achieve a desired work force or output, although, again, variations in driver motor voltage are not taken into account.
The shortcomings of such known control schemes are particularly noticeable in floor conditioning machines that are powered by a rechargeable battery supply. Although a rechargeable battery supply offers some conveniences, the battery voltage applied to the various floor conditioning systems or appliances, and particularly to the driver motor, decays in relation to the energy discharged by the battery and the total time of discharge. Thus, the available mechanical conditioning/working power that may be delivered to the floor varies dependent upon the voltage and current that the battery supply can deliver to the driver motor. That is, mechanical working power (i.e., work output delivered to the floor) is proportional to the power delivered to the driver motor.
Thus, for example, if the driver motor current is held constant, the conditioning work delivered to the floor surface will vary as a function of voltage applied to the driver motor (e.g., the battery voltage). As a result, when the driver motor load current is held constant (as is the case with known control schemes), more working power is delivered to the working appliance (i.e., brush or pad) at the beginning of the battery life cycle, and less working power is available at the end of the battery life cycle as the battery voltage decays. Such variation in mechanical working power delivered to the floor, however, may not be desirable because it can affect the consistency of the work results, particularly when the floor conditioning task is burnishing, and, even more particularly, when the burnishing task is part of a multi-task floor conditioning machine. Accordingly, it would be desirable to provide a floor conditioning system in which the amount of mechanical working power applied to the floor can be controlled at a desired level.